Nylon tubing with braided cover and method of making



R. B. KOCH April 4, 1961 NYLON'TUBING WITH BRAIDED COVER AND METHOD OF MAKING Filed July 28, 1958 ATTORN EYS 2 Sheets-Sheet 1 INVENTOR 4mm. himz BY 0,, rm

R. B. KOCH 2,977,839

NYLON TUBING WITH BRAIDED COVER AND METHOD OF MAKING April 4, 1961 2 Sheets-Sheet 2 Filed July 28, 1958 ANGLE\S{ p lNENTO zfiww ATTORNEYS i United, States NYLON TUBING WITHBRAIDEDCOVEli METHOD F;.-MAKING Robert B. Koch, Reading, Pa; assignor to The Polymer Corporation, Reading, Pa'., .a corporation Pennsylvania Filed July 28, 1958, Ser. No. 751,268

' 25 Claims. c1. 87-1 This invention relates to nylon tubing and is particutent larly concerned with the production of a tubing upon which is applied a braided covering composed of synthetic plastic textile fibres.

The invention is especially useful in connection'with applying a synthetic textile fibre on the outside .of an extruded nylon tube and in bonding the braid to the tube in a manner to be described below. by means of which a tube of great strength, marked flexibility and extremely varied adaptability can be produced.

Extruded nylon tubing is now well known in the art but to my knowledge there; has been no satisfactory ,braided tubing of this ;kind. available to'industry and my invention is particularly concerned with the provision of such a tubing as well as with a method of producing the same, and in its broader aspects the invention contemplates the provision of' tubing of this kind which has a substantially increased burst strength as well as one which has a greater degree of flexibility and a longer Hex-fatigue life expectancy; the provision of such a tubing in which the braided covering material is highly resistant to abrasion; the provision of such a tubing which lends itself with remarkable facility to hot flaring and the application of a flare fitting or coupling; the provision of such a braided tubing in which only those fibres or filaments of the applied braiding which lie near the tube are actually bonded to the tube so that the remaining fibres or filaments outwardly thereof are free 1 to move and slip with respect to one another, which 'I find is an important factor in preventing rigidity and undue physical deterioration due 'to abrasion or wear as between one fibre and another; theprovision of a braided tubing which can be dyed to a desired color during normal manufacturing procedure thereby avoiding any extra operational steps for this purpose; the provision of tubing of the character described which prevents ravelling of the braided cover when the tubing is cut to desired lengths or when subjected to mechanical abrasion in service; the provision of braiding which can be applied in multiple layers without impairing the desirable qualities and characteristics of any layer; and the provision of a method for manufacturing a tubing having the desirable properties and characteristics just I enumerated.

How the foregoing objects and advantages together with such others as may appeal-hereinafter or are incident to :my'i'nvention are attained will nowbe described in connection with the accompanying drawings, wherein "Figure 1 is a sectional-elevational view of apparatus :Piatented Apr; 4, 196 1 2 which I employ in braided tubing; v

Figure 2 is a plan view of Figure 1;

Figure :3 is a section of finished braided tubing partly broken away to illustrate certain details of the construction; i

Figure 4 is an enlarged partial cross section of a tubing having one layer of braided cover; and

Figure-5 .is a view similar to that of Figure 4 but showing a double layer of braiding on the tube. 1

.Basicallyconsidered my inventionresides in the discovery that a braided tubing of the charatcer described can be produced by first passing the tubing through a .bathsof a solvent agent for the tubing which is adapted toplasticize the surface thereof, then applying the fibres of the braid to the tubingwhile the surface is still plasticized by passing the tubing through a braiding machine and subsequently passing the braided tubing through a suitable water bath as will further appear, in order to -cure the; product and remove excess plasticizing solvent. v As indicated, these ;are the basic steps which I employ inthe, manufacture of my improved nylon tube having a braided covering and thissbasic procedure is useful in applying either a nylon braid or a braid of polyester fibre such as those prepared from terephthalic acid and ethylene glycol. However, there are certain minor variations in the technique which may be employed. in the handling of these materialswhich will be explained below but ,for the sake of orderly procedure I will first describe the invention as applied to the pro Kluction of a nylon tube having a covering ofnylon [textile fibres.

In the manufacture of nylon tubes having nylon textile coverings I have found that excellent results can be obtained by employing high molecular weight linear polyamides for both the tube and the braid. Of these, polyhexamethyl'ene' adipamide and polymerized epsilon caprolactam, are especially useful with the present invention and, therefore, are preferred. Furthermore, polycaprolactam seems to be somewhat superior because of its greater toughness and higher resistance to flex fatigue although both are satisfactory.

The first step in 'thebasic technique which I have developed for use in manufacturing my improved product is to plasticize the surface of the tube and to this end I prepare a bath of a suitable plasticizing agent, pref erably an aqueous solution of resorcinol because I have found that excellent results can be obtained with this material. The bath is placed in a suitable tank 7 which is provided withheating means 8 so that the resorcinol bath 9 may be kept at any temperature desired. The tank is preferably provided with a cover 10 through which a specific gravity gauge 11 may be inserted into the bath in order to determine the specific gravity of the bath. For best results I have discovered that the resorcinol should have a specific gravity ranging between 1.045 and 1 .051 when the resorcinol is at a temperature of The specific gravity will change with the temperature and the higher the temperature thelower the specific gravity. It might alsobe noted that evaporation of water will increase the specific gravity of the resorcinol bath. In order to prevent too rapid evaporation it is suggestedthat the surface of the bath be covered with polyethylene balls to a depth of approximately inch. Such balls will float on the bath and prevent rapid evaporation of v the water. A metallic cover can also be used to accomplish the same purpose;

The nylon tubing 12 is introduced at the left o tank as viewed in Figures 1 and. 2 and, is passed dqwn under the guide rollers l3 which' are arrangedtohold the tube under the surface of the bath. The direction the manufacture of my. improved r of travel, of course, is'from left to right as indicated by the. arrows in Figure 1.

As shown in the drawings the tank is relatively long in relation to its depth but this relationship can vary as may be convenient in practice, the controlling factor being that the plasticizing action of the resorcinol factor being that the plasticizing action of the resorcinol on the surface of the tube is a timeatemperature relationship. If the bath is relatively cool, say in the neighborhood of room temperature, it is necessary, of course, that the tubing remain in the bath 'for a greater period of time than may be necessary with elevated temperatures. The matter of temperature will be discussed more fully hereinafter.

After the surface of thetube is properly plasticized it leaves the resorcinol tank and passes directly into a suitable braiding machine 14 which may be of any desired type familiar to the art. I have employed for this purpose a 24-carrier War-dwell braider and the results obtained have been highly satisfactory. However, it is obvious that any suitable type of braiding machine may be used.

The braiding angle at which the fibers are applied to the tube is not of the essence of the invention insofar as its basic characteristics are concerned but the use to which the finished product is to be put will dictate to some extent the braiding angle which will yield the best product for that particular purpose. From a practical standpoint the braid angle may vary from somewhere near 28 to as much as 50 or even somewhat more. I prefer to apply the braid at a 42" angle.. The braiding angle is known as the helix angle and with an angle ranging between 38 and 42, very little stretch or shrinkage of the tube will occur when the tube is under internal pressure. Increasing the helix angle above 42 tends to cause a contraction of the tube when under internal pressure and lowering the helix angle below 38 tends to cause elongation of the tube when under pressure. Certain experimental results also indicate that the burst strength of the tube may drop off somewhat when the helix angle falls below 34 or goes much above 50. Between these limits, apparently, the burst strength remains substantially constant.

The matter of the braiding or helix angle assumes considerable importance as compared, for example, with the eflect of the braiding angle for hose which carries the familiar metallic braid. With metallic braid, increase or decrease in the length of the tube tends to damage the wire due to the rubbing or abrading effect which is set up when the strands of the wire rub over one another. This difliculty is completely overcome with the braided tubing of my invention because the braid material is highly resistant to abrasion so that the fatigue characteristics of my improved product will be found to be many times better than in the case of old style. hose braided with metallic strands.

After the braiding operation the braided tube 12a may be passed over a Wheel 15 and then led through a curing zone which, in my preferred practice, takesv the form of a fiat elongated tank 16 containing a bath of hot water 17, the braided tubing passing under suitable guide wheels 18 in the tank which serve to hold the tubing under the surface of the bath.

The effect of the bath is to cure the product by removing any excess plasticizing agent which may be prescut so as to avoid possible later degradation of the fin,- ished product. The action of the bath is two-fold: (1) excess resorcinol is dissolved by the hot water'and there by removed and (2) the heat of the bath increases the plasticizing effect of the resorcinol. This tends to more deeply plasticize the surface of the nylon tube and at the same time, to plasticize the fibers of the braid which are in close proximity to the surface of the tube. In this way a strong bond is created by virtue of the fusion of these two surfaces. It should also be noted that the effect. of the water bath may also be visualized as aiding in the removal of excess resorcinol by enabling it to react more readily both with the nylon intercore and the fiber applied thereto. What happens, apparently, is that a certain precentage at least of the resorcinol is thereby drawn away from the surface and consumed in effecting the bond.

The temperature of the water bath 17 should be maintained somewhere between F. and 212 F. and preferably near F. because I have found that this temperature yields excellent results.

The period of time during which the braided tube remains in the water bath, of course, will depend upon its temperature and the quantity of excess plasticizing agent which may have to be removed. Therefore, the size of the hot water tank will have to be related to the speed of travel of the braided tube so that it will remain in the heating bath sufficiently long to accomplish the desired results. After the heat is applied and curing is complete, the braided tube, of course, can be passed out of the bath and dried to remove moisture and then run to whatever form of storage may be appropriate or desired.

Use of this water bath curing zone gives rise to an additional advantage in that, where a change in color of the finished product is desired, a dye can be incorporated in the bath so that the color can be applied at the same time that the curing is taking place, thereby eliminating extra operations.

At this point I should like to say that in applying a nylon braid to a nylon tube it may sometimes be desirable to apply more than one layer of braided covering and I have found that this can be done quite readily simply by repeating the procedure already described, namely, by again treating the tube with its first braided covering in a resorcinol bath and then again braiding and curing as already described.

I should now like to return to the matter of temperature employed in the resorcinol bath. In procedures involving the application of a nylon braid to a polyhexamethylene adipamide-type of nylon tube it is quite possible to employ the bath without heating it, i.e., to proceed at room temperature. However, since the effect of the bath is based upon a time-temperature relationship, operations at room temperature may be too slow for certain manufacturing techniques. For instance, the length of the tank 7 may have to be too great or the rate of travel may have to be too slow. For this reason, I prefer to heat the resorcinol as described and for polyhexamethylene adipamide tubes excellent results can be secured with a resorcinol bath of from 140 F. to 160 F. While for the polycaprolactam type it is better to use a somewhat higher temperature, say up to the neighborhood of 180 F.

Since the purpose of the bath is to plasticize the surface of the tube, the tube must be permitted to remain in the bath at whatever temperature may be employed until such time as there is sufiicient plasticizing effect to enable the soft surface to develop a bond with those fibres of the braid which are relatively near or in contact with the surface. Outwardly of this region the other fibres of the braid are not coated with or embedded in the plastic surface so that they do not lose their ability to move freely one over another and, therefore, do not in any way impair the flexibility of the braid as a whole. The technique I employ with my invention lends itself extremely well to securing this result because I have found that plasticization is not sufiieient to involve more than the first few layers of the braid. Thus substantially all of the fibres beyond or on the outside of the bonding zone are free to move and slip one over another. As aconsequence the braided tube retains its flexibility and has a greater flex-fatigue life than a' product in which all ofthe. individual strands. or

fibres'arebonded to oneanotherin addition to having the inner layers bonded to the tube itself.

.I haveattempted to illustrate in Figures 3 to 5, in-

elusive, thenature of the structural relationship which In FigureS a second layer of braiding has been applied to a first layer and in this figure the outermost layer of fibres of the first layer are plasticized as indicated at 12bb, the inner fibres of the outer cover which lie near to the plasticized outer layer of the inner cover being indicated at. 12cc and the final layer of fibres of the outer braid cover which are free to move one over another being indicated by the character 12dd. b

In connection with Figures 3 to 5, inclusive, and particularly in connection with Figures 4 and 5,it will be understood, of course, that the showing is diagrammatic and greatly enlarged, and that the size relationships of the several layers are considerably exaggerated in order to give a clearer understanding of the natureof the results. secured with my invention. It will be understood also that in applying a. second braided layer to a first braided layer only those fibers near the outside of the first braided layer are plasticized by the resorcinol bath so that there is very little, if any, impairment of the flexibility of the finished product. In other words, th e fibres of the first braided layer which lie between the two plasticized regions are in no way bonded together and remain free to move one with respect to another. p

At this point I should like to say that in applying a second braided layer to a first braided layer I have found it best, even in the case of a polyhexamethylene adiparnide tube, not to attempt operations at too low a temperature, because better results are secured with a heated resorcinol bath. Indeed, a heated bath is essential when applying a second layer of caprolactam braid since theresorcinol will not adequately plasticize caprolactam material unless 1 the bath is heated as indicated above. By employing a resorcinol bath at an elevated temperature in accordance .With the teachings before given, it is possible in applying a second layer, to proceed exactly in accordanceiwith the instructions for applying the first layer. The technique so far described, as indicated, isparticularly useful in applying a nylon braid to a nylon tube. However, it can also be employed in applying a'braid of polyester fiber such as-those prepared from terephthalic acid and ethylene glycol despite the fact that the resorcinol bath has no plasticizing effect upon fibers of this kind. In View of this the bond which is obtained is'not of thesame character, i. e., it does not involve a fusion between the tube surface and the fibres but is purely a physical or mechanical type of bond. For this reason, it is important'to be sure that the surface of the. tube or inner core is very thoroughly plasticized and preferably to a greater degree than may be necessary'in applying a nylon braid. Therefore, with braids of this type, it is important to employ the resorcinol bath at a temperature near the upper limits set forth above and preferably at a temperature close to 180 F. In this way the plasticized layer on the nylon tube may be sufliciently deep to thoroughly penetrate around the first few layers of braid fibres. This yields a very satisfactory bond for many purposes and leaves the outer layers of the braid free to slip one over another as before.

In applying braids prepared from terephthalic acid and ethylene glycol the distance between the point at which the tube leaves the resorcinol bath to the braiding point should be kept at a minimum so that the time in transit is not great enough to permit possible loss of plasticity. This will help to ensure a good bond. t

It should be noted in connection with fibres made from ter'ephthalic acid and ethylene glycol that the application of a second layer of braid is not practical with the technique disclosed hereinsince the resorcinol bath has no plasticizing effect upon fibers of this kind.

Another feature of my invention is the possibility of using a braid containing a mixture of nylon and polyester fibres of the character mentioned. Such a mixture yields a number of advantages in addition to those already enumerated For instance a polyester fibre prepared from terephthalic acid and ethylene glycol has somewhat greater strength than nylon as well as being somewhat less elastic. A blend of the two fibres, therefore, will result in a product having a somewhat greater burst strength. However, it may be slightly less flexible but for some purposes this would not be an objectionable factor. A blend or mixture of the two types of braiding material may vary widely insofar as the content of each is concerned, but I have found that good practical results are obtainable with blends containing anywhere from 5% to 50% of nylon. The nylon, of course, will lend itself to a fusion type of bond as described above and this would be obtainable to a greater or less degree depending upon the percentage of nylon which may be included. Afusion type of bond, obviously, is somewhat. more secure than is a purely mechanical type of bond so that the determining factor in deciding upon the percentage of nylon to be included in a blended braid would be the degree of fusion bonding. that may be desirable for the purpose to which the finished product is to be put. 7

It will now be appreciated that nylon tubing braided in accordance with the present invention will be strong and flexible. It will lend itself with remarkable facility to flaring and the application of flare fittings or couplings so that various lengths of tubing can be connected together as may be required to meet specific conditions. The braid will not ravel when the tube is cut to desired lengths or when the braided surface is subjected'to mechanical abrasion sufficient to cause a break. Finally it is readily adaptable to a wide variety of uses and in fact, .can take the place of other and less desirable types of braided tubing presently available in the art. For a given purpose it can be madev with a much smaller overall dimension without impairment of its carrying capacity and as a consequence it will weigh less than other types of braided tubes. i

. Iclaim: i V

' 1.' The method of applying a braided textile covering to the surface of nylon tubing, the covering being chosen from the class consisting of high molecular weight syntheticlinear polyamide and polyester textile. fibres, which method comprises passing the tubing through a bath of a solvent agent for the tubing adapted to plasticize the surface thereof, then applying the said fibres by passing the tubing through a braiding machine while the surface is still plasticized, and passing the braided tubing through an aqueous bath adapted to remove excess solvent and cure the product. "'2. 'The method of claim 1. wherein-the-solvent isa bath of resorcinol.

3. The method of claim 1 wherein the solvent is a bath of resorcinol heated to a temperature of from F. to 180 F.

4. The method of claim 1 wherein the curing bath is heated to a temperature not less than F. I

5. The method of applying a nylon braid on a nylon tube which comprises passing the tube through a resorcinol bath to plasticize the surface, applying the braid to the tube after it leaves the bath and while the surface is still plasticized, and then passing the braided tube through a hot water bath.

6. The mehod of claim 5 wherein the resorcinol bath is heated to from 140 F. to F.

7. The method of claim wherein the temperature of the water bath is maintained between 150 F. and 212 F.

8. The method of claim 6'wherein the water bath is maintained between 150 F. and 212 F.

9. The method of applying nylon braid on a nylon tube which comprises passing the tube through a bath of an agent adapted to plasticize the surface of the tube, passing the tube through a braiding machine while the surface is still plasticized, and passing the braided tube through an aqueous bath adapted to remove excess plasticizing agent and cure the product.

10. The method of claim 9 wherein the braid is applied at a helix angle of from 28 to 50.

11. The method of claim 9 wherein the braid is applied at a helix angle of 42.

12. The method of claim 1 which also includes application of a second braid layer on said first applied layer by passing the braided tube through a bath of a solvent agent for the fibres of the first layer to plasticize the surface thereof, then passing the tube through a braiding machine while the surface of the first braid layer is still plasticized, and then passing the tubing with both braids applied through an aqueous bath adapted to remove excess solvent and cure the product.

13. The method of claim 1 in which the covering includes fibre made from terephthalic acid and ethylene glycol, and further, wherein the solvent is a bath of resorcinol heated to from 140 F. to 180 F.

14. A method of applying a synthetic fibre braid to the surface of nylon tubing where the tubing is chosen from the class which consists of polyhexamethylene adiparnide and polymerized epsilon caprolactam and the 'braid fibre is chosen'from the class which consists of the same but including also polyester fibre prepared from terephthalic acid and ethylene glycol, said method comprising passing the tubing through a bath of resorcinol to plasticize the surface thereof, then applying the said fibres by passing the tubing through a braiding machine while the surface is still plasticized, and passing the braided tubing through a heated water bath to remove excess resorcinol and cure the product.

15. A method according to claim 14 wherein the resorcinol bath is heated to a temperature of from 140 F. to 180 F.

16. A method according to claim 15 wherein the water bath is heated to a temperature of from 150 F. to 212 F.

17. A method according to claim 14 wherein the water bath is heated to a temperature of from 150 F. to 212 F.

18. A method of applying a synthetic fibre braid to the surface of polyhexamethylene adipamide tubing, the fibre being chosen from the class which consists of polyhexamethylene adipamide and polymerized epsilon caprolactam, said method comprising passing the tubing through a bathof resorcinol at room temperature to plasticize the surface thereof, then applying the said fibres by passing the tubing through a braiding machine while the surface is still plasticized, and passing the braided tubing through a heated water bath to remove excess resorcinol and cure the product.

19. As a new product nylon tubing carrying a braided and fibers made from terephthalic acid and ethylene glycol, the covering being composed of a plurality of superimposed filament layers with layers lying close to the surface of the tube being bonded thereto and layers lying outwardly thereof being free to move and slip with respect to one another.

20. As a new product nylon tubing carrying a braided textile covering from the class consisting of high molecular weight linear polyamides, the covering being composed of a plurality of superimposed filament layers, with layers lying close to the surface of the tube being bonded thereto and layers lying outwardly thereof being free to move and slip with respect to one another.

' 21. A product according to claim 20 wherein a second braided covering overlies the first with the inner fibres of the second being bonded to the outer fibers of the first.

22. A product according to claim 19 wherein the content of nylon fibres in the braiding is from 5% to 50% of the total.

23. As a new product, nylon tubing carrying a braided nylon textile covering, said covering being composed of a plurality of superimposed filament layers with layers lying close to the surface of the tube being fused thereto and layers lying outwardly thereof being free to move and slip with respect to one another.

24. The method of applying a synthetic fiber braid to the surface of nylon tubing which comprises subjecting the tubing to the action of a solvent agent adapted to plasticize both the tubing and the braid, continuing the treatment until the surface of the tubing is plasticized, then applying the braid to the tubing while the surface is still plasticized, and then removing excess plasticizing solvent and curing the product.

25. As a new product, nylon tubing carrying a braided textile covering from the class consisting of high molecular weight linear polyamides, said covering being composed of a plurality of superimposed filament layers, with layers lying close to the surface of the tube being fused thereto.

References Cited in the file of this patent FOREIGN PATENTS 855,058 France Feb. 5, 1940 Great Britain Sept. 5, 1938 

